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Labs July 2012
I must be out of my mind. Am I confused? Would I know? Who in their right mind sits down and writes things like this for the fun of it? Did I get all my meds for today? Can I at least have one hand loose?
This one took a while to put together, as it required a lot of looking-up on the part of the preceptor. Got to love the web!
As usual, please remember that this article is not meant to be the final word on anything, or even comprehensive in any way. Nurses at the bedside have to work on the fly, and the things that they need to keep in their heads have to be practical and brief – not that this article is very brief, but hopefully the items are. This information is supposed to reflect what a preceptor might teach a new orientee, or maybe to answer some of the questions that the orientee might come up with. Each item in this article is backed up by (apparently) an average of not less than eight thousand pages of reference material in 37 different languages – I just tell what I know! Please make sure that you check your own references to verify lab/drug and toxic ranges!
Let us know when you find errors, and we’ll fix them up right away. Thanks!
Update note: holy cow, this one was torture. Useful tip: remember that if you’re reading this article online, or on your computer, you can click on any of the images, grab a corner, and pull to make the image bigger, easier to see.
What are some of the labs that we follow on our patients in the MICU?
1- Chemistries
1-1- The basics: “Chem 10”
1-1-1: Sodium, including Free Water Deficits, and an Extremely Important Thing
1-1-2: Potassium
i. What does “hemolyzed” mean?
ii. A hemolyzed potassium story…
1-1-3: Magnesium
1-1-4: Chloride
1-1-5: Bicarb
1-1-6: BUN
1-1-7: Creatinine
1-1-8: Glucose
i. Acetone
ii. HbA1C
1-1-9: Calcium
i. Ionized Calcium
ii. Corrected Calcium
iii. Calcium and Citrate Toxicity
1-1-10: Phosphorus
1-2- Some other basic chems:
1-2-1: Lactate
1-2-2: Osmolality
1-2-3: Amylase
1-2-4: Lipase
1-2-5: Ammonia
1-2-6: Albumin
1-3: Renal Labs
1-3-1: Creatinine Clearance
1-3-2: Uric Acid
1-3-3: Myoglobin
1-3-4: Urinalysis
1-3-5: 24-hour urine collections
1-3-6: urine electrolytes
1-4: Drug Levels
1-4-1: Dilantin
1-4-2: Valproate
1-4-3: Tegretol
1-4-4:Lithium
1-4-5:Theophylline
1-4-6:Thiocyanate
1-4-7: Vancomycin
1-4-8: Gentamicin
1-4-9: Digoxin
1-4-10: Tacrolimus, cyclosporine
1-4-11: Peaks, Troughs, and Random Levels
1-5: Tox Screen Panel Meds
1-5-1: Tylenol
1-5-2: Salicylates
1-5-3: Opiates
1-5-4: Cocaine
1-5-5: Benzodiazepines
1-5-6: Ethanol
1-5-7: Methanol
1-5-8: Ethylene glycol
1-5-9: Miscellaneous
1-5-10: A really cool thing.
1-5-11: A scary story…
1-6: Cardiac Labs
- Electrolytes
1-6-1: Potassium
1-6-2: Magnesium
- Cardiac Enzymes
1-6-3: What are cardiac enzymes?
1-6-4: Which cardiac enzymes do we follow on our patients?
1-6-5: Can a patient have elevated enzymes without having an MI?
1-6-6: Can a patient have an MI without having elevated enzymes?
1-6-7: What is CPK again?
1-6-8: What is the reference range for CPK?
1-6-9: What are isoenzymes?
1-6-10: What is the “MB fraction”?
1-6-11: What are MM and BB?
1-6-12: Does a higher CPK mean a larger MI?
1-6-13: How many CPKs should be drawn, and how far apart?
1-6-14: What is troponin?
1-6-15: What is the reference range for troponin?
1-6-16: How often should troponins be drawn, and how far apart?
1-6-17: What is “washout”?
1-6-18: Can cardiac enzymes go up if a patient is ischemic, but not having an MI?
1-6-19: What is hBNP all about?
1-6-20: What is C-reactive protein all about?
1-7: Lipids
1-7-1: Total Cholesterol
1-7-2: HDL
1-7-3: LDL
1-7-4: Triglycerides
2- Respiratory Labs:
2-1: ABGs:
2-1-1: pO2
2-1-2: pCO2
2-1-3: pH
2-1-4: bicarb
2-2: VBGs
2-2-1: Can I believe what a VBG tells me?
2-2-2: What are central venous sats all about?
2-2-3: What’s the difference between a central venous sat and a mixed venous sat?
2-2: Carboxyhemoglobin
2-3: Methemoglobin
2-4: What is an anion gap, how do I calculate it, and why is it listed here under “respiratory” labs?
2-4-1: Acidoses
2-4-2: Alkaloses
2-4-3: Calculating the Gap
2-5: Alpha-1 Antitrypsin
3- Liver Function Tests
3-1: A story.
-3-1-1: Cherry blossoms
3-2: Bilirubin: direct, indirect, total
3-3, 4: ALT, AST
3-5: Alkaline Phosphatase
3-6,7: PT and PTT (Why are these here?)
3-8: SPEP
3-9: Hepatidites
3-9-1: Hepatitis A
3-9-2: Hepatitis B
3-9-3: Hepatitis C
4 – Hematology
4-1: Hematocrit
4-2: White count
4-2-1: the differential
4-2-2: A true saying
4-3: Platelets
4-3-1: Heparin-Induced Thrombocyopenia
4-4: Coagulation Studies
4-4-1: PT
4-4-2: PTT
4-4-3: INR
4-5: D-dimer
4-6: DIC screen
4-7: Fibrin Split Products
4-8: Fibrinogen
4-9: ESR
4-10: Coombs test
5- ID
5-1: Cultures
5-2: Sensitivity Reports
5-3: Some specific tests:
5-3-1: TB/ AFB’s
5-3-2: Influenza
5-3-3: H5N1 Avian Flu
5-3-4: HIV testing/ CD4 count
5-3-5: Viral Load
5-3-6: CMV
5-3-7: RSV
5-3-8: Herpes testing
5-3-9: Branch-chain DNA and PCR
5-3-10: Kary Mullis
5-3-11: Lyme Disease and Babesia
5-4: CSF
5-4-1: Which kind of infection?
5-4-2: Some normal values for CSF
5-5: Opportunistic Infections in the MICU
5-5-1: MRSA
5-5-2: VRE
5-5-3: What are survey swab studies all about?
5-5-4: C.difficile
5-5-5: A suggestion for a study – should ICU nurses be routinely screened to see if they’re carriers of opportunistic infections? Anyone doing a Master’s?
6- Endocrine
6-1: Thyroid Studies
6-2: “Cort-stim” tests
6-3: Testosterone
6-4: Beta HcG
7- Immunology
7-1: A New Discovery - “Anti-RN” Antibodies
7-2: ANA
7-3: ANCA
7-4: Rheumatoid Factor
7-5: Scleroderma Antibody
7-6: Immunoglobulins
10- Odds and Ends:
10-1: Tumor markers
10-3-1: PSA
10-3-2: CEA
10-2: Haptoglobin
11- A nice picture.
12- Collecting lab specimens:
12-1: Blood Draws
12-1-1: peripheral sticks
12-1-2: specimens from arterial lines
12-1-2-1: ABGs
12-1-2-2:Other labs
12-1-3: specimens from central lines
1- VBGs/ CV sats
2- What is a “true” mixed venous specimen?
12-1-4: blood cultures
12-2: Urines
12-2-1: UA specimens
12-2-2: Urine cultures
12-2-3: 24-hour urine collections
12-3: Sputum Specimens
12-4- Stool specimens
12-4-1: stool for O&P
12-4-2: stool for C.diff
12-4-3: stool for occult blood
What are some of the labs that we follow on our patients in the MICU?
There are a lot of labs out there, and they come in a wide variety of flavors. If you never got comfortable with frequently looking up lab results on the floors, you're probably going to have to get over that one quickly, since watching trends of one kind or another is about 90% of what we do in the ICU: labs, vital signs, effects of meds, transfusions – it all makes a dynamic picture that you have to learn to grasp, and follow as it changes.
The basic idea is often really easy: if some lab value is way out of line, then something having to do with the patient probably is too. Doh! You don't want to be wrong about this, which is why the team will sometimes ask you to re-send a spec. Which of course is frustrating when you think that your GI-bleed patient isn't losing his blood pressure because he forgot to drink his Gatorade this morning or something...
Remember that basic physiology thing about how the body is made up of subsystems? That sort of basic sort of thing? The labs reflect those systems and how they're doing (or not doing) at whatever it is that they're meant to do. Simple example: if the kidneys aren't clearing nitrogenous wastes from the blood, then the levels of those wastes will rise – makes sense to interpret that as kidney failure, right?
But nothing is ever as simple as you'd like it to be. My son and I just bought an elderly motorcycle...(What? What do you mean, "Don't talk about the motorcycle"?... What do you mean, "it has nothing to do with the topic"?... It's got plenty to do with the topic...you're just jealous, ‘cause...
What do you mean, you "wouldn't get on that thing even if"?… so we had two quads in the unit last month, so what?!)
Anyway, for the ICU newbie there's lots to learn, as usual, and also as usual the best thing is just to try to get some idea of what you're looking for, and then to accumulate mileage and experience – then the things that you learn by reading will make lots more sense. This is a pretty important point: don’t try to memorize it all at once – come back and re-read this article a year from now. This is especially true when it comes to motorcycles. See, the float bowl in the carburetor... ow!
1- Chemistries:
There’s lots of chemistries out there, but the basic ones are always easy to get, and can give you lots of clues about what you're looking for. Maybe I can get one of the kids to draw the little diagram thingy.
Now here's the thing – every day these kids come home from school:
"Hey kids, whad’ya learn at school today?"
"Nothing." And man, you can sit there and ask them about school until your jaw just drops right off, but they just won't tell you a thing. Then later, daughter # 2 wanders by where I'm struggling to do some (probably) really easy thing with the word processor, and she says: "Dad!! Use a text box!"
The preceptor: "What's a text box?"
D # 2: "Here, just get up and let me show you." Eight lightning moves follow, a nice box or line drawing (as below) appears, and I'm still in the dark. Nice drawing, but still in the dark. I never did that to my parents, not once. Except that time with the cable box.
Na+ CL BUN
glucose
K+ CO2 Creatinine
Right – this is the little electrolyte drawing gatsy, which makes it easy to remember the values that you want to write down someplace quickly, like on your scrub pants. This is one of those doctor-ish things that nurses hate, but actually (like lots of other things) it isn't hard to learn at all – seven items? And you use them all the time anyhow, or most of them anyway – and it makes things easy to write down.
Let's take these guys one at a time, and please remember that all this info is strictly "from the hip" - I mean, you can keep on going and going with this stuff, and pretty soon you're an endocrine fellow or something. So all this stuff is "with a lot of lies thrown in", as they say.
1-1- the basics: “Chem 10”
1-1-1: Sodium/ Na+ (135 - 145 meq/l):
Sodium is confusing – like lots of things in the physiology world, it doesn't always do what you think it's going to do, or what you want it to do. I guess lots of things are like that. In fact, the motorcycle ...ow!
The basic idea is that sodium is a solute, floating around in the serum solvent. If Izzy Shmulewitz has a TIA, and lies on his bed for three days before his no-good bum of a son-in-law comes to check on him, he's going to get very – what? Very dry – dehydrated, mostly from "insensible loss" - I think that you lose something like a liter and a half every day this way, mostly through breathing and sweating. And that's when things are normal – imagine what happens to marathon runners. No wonder they don't look so good at the end. "Pruned."
Anyway, if some of the solvent goes away, that leaves more solute in what remains, correct? So if you measured Izzy's sodium before his TIA, it might've been something like 138. After three days of not drinking anything, it might be in the 150's. Too high! All sorts of unpleasant things can happen – seizures, drain bamage, renal failure (why?), and so on.
Here’s a formula for figuring out exactly how dry they are (the water they should have, but don’t have, is the “Free Water Deficit”. No screaming now – I know it’s math, but it’s not so bad.
Free Water Deficit = (0.6 x pt’s weight in kg) x [(pt’s sodium / 140) –1.0]
So let’s try it in steps: say the patient weighs 70 kg, and his sodium is 160 (oof – he’s dry!)
First step: 0.6 x 70kg = 42
Step two: His sodium is 160, divide that by 140, that gives 1.14. Subtract 1.0 from that, you get .14
Last step: 42 x .14 = 5.9 liters. Call it six liters. That’s about 13 pounds.
That’s a lot of liters, in case anybody’s counting. Try it sometime.
What about other way? What if Shmulewitz turns out to be one of those people, (like my dad), who insists on drinking eight glasses of water a day? And what if his doctor puts him on a diuretic, say twice a day for his swollen ankles, because he won't stop drinking them ("Gotta flush the kidneys!")?
(This next part is probably mostly lies, but it was explained to me this way once): it turns out that the loop diuretics make you dump not just potassium, but all the other cations that float around dissolved in the serum : sodium and hydrogen come to mind. (In fact, whenever you hear the word "diuretic", you should immediately respond in your head with "K+ !". Check the patient’s creatinine before you give any. Why?)
Apparently people dump enough sodium in urine in response to diuretics to cause a significant drop – actually, I was told that you pee half-normal saline. What if you now replace the lost volume with pure water – tap water, or bottled? No electrolytes in it at all. You can see what's coming, right? - having dumped lots of sodium, Izzy now takes in lots of solute, and both of these maneuvers make his sodium drop a whole lot. If the solute levels get too low, water may start moving into the third space ("Head for the third space, Mr. Spock." One eyebrow goes up: "Um, captain, can I pee first?"). Gatorade! (Who is that Picard guy, anyhow?)
(Losing a lot of hydrogen can produce bad things too – several days of diuresis will usually produce an alkalosis, because it leaves a lot of bicarb floating around with no hydrogen dancing partners – they all got peed out. Because the patient's fluid volume has "contracted", they call this a "contraction alkalosis". Easier to call it a “diuretic alkalosis”, but no…)
"Third - spacing" of fluid into the brain tissue in response to hyponatremia can result in a rising intracranial pressure. I hate it when that happens – all sorts of unpleasant things can result, right? Including, possibly, herniation. Ack! Quick now – what's the first sign of rising intracranial pressure?
Back to the patient. So – what to do? Hypernatremia usually means that a lot of circulating volume has been lost – give some back! Hyponatremia? - got too much volume going around? Restrict fluid intake for a few days and the patient should straighten out. Might want to give some hypertonic saline, usually as 3% saline, in case overdiuresis or something has caused too much sodium loss.
Now comes an extremely important thing. Try very hard to remember this. Can anybody pronounce the following?: "Central Pontine Myelinolysis". This is a truly awful result of too rapidly correcting a hyponatremia, in which crucial parts of the pons (in the midbrain, is it?) become de-myelinated. Stripped. Leaving the patient possibly quadriplegic, possibly comatose, possibly (shudder) "locked-in". Oh yeah, and maybe dead. Possibly preferable.